Enhanced vehicle navigation using non-destructive inspection one-dimensional sensor arrays

Abstract

Systems and methods for tracking the location of a non-destructive inspection (NDI) scanner using scan data converted into images of a target object. Scan images are formed by aggregating successive scan strips acquired using one or two one-dimensional sensor arrays. An image processor computes a change in location of the NDI scanner relative to a previous location based on the respective positions of common features in partially overlapping scan images. The performance of the NDI scanner tracking system is enhanced by: (1) using depth and intensity filtering of the scan image data to differentiate features for improved landmark identification during real-time motion control; and (2) applying a loop-closure technique using scan image data to correct for drift in computed location. The enhancements are used to improve localization, which enables better motion control and coordinate accuracy for NDI scan data.

The invention claimed is: 
     
       1. A method for tracking a location of a scanner having a one-dimensional sensor array in a frame of reference of a target object, the method comprising:
 (a) setting filter threshold values for depth and intensity which are associated with a specific type of feature; 
 (b) moving the scanner across a surface of a target object from a starting location to an ending location along a path; 
 (c) acquiring successive sets of sensor data at a known capture rate as the scanner moves along the path during step (b); 
 (d) converting the successive sets of sensor data to respective scan strips of scan image data; 
 (e) constructing successive scan images from respective sequences of scan strips converted from sensor data acquired as the scanner moves along the path during step (b); 
 (f) filtering the successive scan images using the filter threshold values to isolate the feature of the specific type, wherein the path along which the scanner moves during step (b) is adjusted based on results of the filtering; 
 (g) finding feature points in respective pairs of successive scan images; 
 (h) determining which feature points found in step (g) are common feature points in the respective pairs of successive scan images; 
 (i) computing pixel position differences between respective positions of common feature points in the respective pairs of successive scan images; 
 (j) computing respective scanner displacements by multiplying the respective pixel position differences computed in step (i) by a scaling factor representing a distance traveled by the scanner per scan strip; and 
 (k) computing coordinates of successive positions of points on respective portions of the surface of the target object corresponding to the successive scan images based on the respective scanner displacements. 
 
     
     
       2. The method as recited in  claim 1 , further comprising:
 (l) comparing respective scan images corresponding to the start and ending locations of the scanner; 
 (m) determining a location offset of the ending location from the starting location; and 
 (n) computing corrected coordinates of successive positions of points on the respective portions of the surface of the target object corresponding to successive scan images based on the location offset. 
 
     
     
       3. The method as recited in  claim 2 , further comprising:
 (o) associating the corrected coordinates with the successive scan images; and 
 (p) storing the successive scan images and associated corrected coordinates in a non-transitory tangible computer-readable storage medium. 
 
     
     
       4. The method as recited in  claim 3 , further comprising:
 (q) computing corrected angles of successive orientations of the respective portions of the surface of the target object corresponding to the successive scan images based on the location offset; and 
 (r) associating the corrected angles with the successive scan images, 
 wherein step (p) further comprises storing the associated corrected orientations with the successive scan images and associated corrected coordinates in the non-transitory tangible computer-readable storage medium. 
 
     
     
       5. The method as recited in  claim 1 , wherein the feature is an edge at a specified depth range. 
     
     
       6. The method as recited in  claim 1 , wherein the feature comprises series-connected edges that form a closed loop. 
     
     
       7. The method as recited in  claim 1 , wherein step (i) comprises computing the pixel position difference by counting a number of pixels by which the position of the common feature point in one scan image is offset from the position of the common feature point in another scan image which partially overlaps with the one scan image. 
     
     
       8. The method as recited in  claim 1 , further comprising computing the scaling factor by dividing a speed of the scanner by the known capture rate. 
     
     
       9. A method for tracking a location of a motion platform carrying first and second scanners that respectively comprise first and second one-dimensional sensor arrays which have respective mutually parallel centerlines separated by a fixed distance, the method comprising:
 (a) setting filter threshold values for depth and intensity which are associated with a specific type of feature; 
 (b) moving the first scanner across a surface of a target object from a starting location to an ending location along a path; 
 (c) operating the first scanner to acquire a first sequence of sets of sensor data at a known capture rate as the first scanner moves along the path; 
 (d) operating the second scanner to acquire a second sequence of sets of sensor data at the known capture rate as the first scanner moves along the path; 
 (e) converting the first sequence of sets of sensor data to a corresponding first sequence of scan strips of scan image data; 
 (f) converting the second sequence of sets of sensor data to a corresponding second sequence of scan strips of scan image data, wherein a number of scan strips in the second sequence of scan strips is the same as a number of scan strips in the first sequence of scan strips; 
 (g) constructing successive first scan images from the first sequence of scan strips; 
 (h) constructing successive second scan images from the second sequence of scan strips; 
 (i) filtering the first and second scan images using the filter threshold values to isolate the feature of the specific type, wherein the path along which the first scanner moves during step (b) is adjusted based on results of the filtering; 
 (j) finding feature points in the first and second scan images; 
 (k) determining which feature points found in step (j) are common feature points in the first and second scan images; 
 (l) computing a pixel position difference between the respective positions of a common feature point in the first and second scan images; and 
 (m) computing a scanner displacement by multiplying the pixel position difference computed in step (l) by a scaling factor representing a distance traveled by the first scanner per scan strip. 
 
     
     
       10. The method as recited in  claim 9 , further comprising:
 (n) comparing respective first scan images corresponding to the start and ending locations of the first scanner; 
 (o) determining a location offset of the ending location from the starting location; and 
 (p) computing corrected coordinates of successive positions of points on the respective portions of the surface of the target object corresponding to successive first scan images based on the location offset. 
 
     
     
       11. The method as recited in  claim 10 , further comprising:
 (q) associating the corrected coordinates with the successive first scan images; and 
 (r) storing the successive first scan images and associated corrected coordinates in a non-transitory tangible computer-readable storage medium. 
 
     
     
       12. The method as recited in  claim 11 , further comprising:
 (s) computing corrected angles of successive orientations of the respective portions of the surface of the target object corresponding to the successive first scan images based on the location offset; and 
 (t) associating the corrected angles with the successive first scan images, 
 wherein step (r) further comprises storing the associated corrected orientations with the successive scan images and associated corrected coordinates in the non-transitory tangible computer-readable storage medium. 
 
     
     
       13. The method as recited in  claim 9 , wherein the feature is an edge at a specified depth range. 
     
     
       14. The method as recited in  claim 9 , wherein the feature is a comprises series-connected edges that form a closed loop. 
     
     
       15. The method as recited in  claim 9 , wherein step (l) comprises computing the pixel position difference by counting a number of pixels by which the position of the common feature point in one first scan image is offset from the position of the common feature point in one second scan image which partially overlaps with the one first scan image. 
     
     
       16. A system comprising:
 a motorized motion platform comprising a frame; 
 a scanner comprising a one-dimensional sensor array supported by the frame; and 
 a computer system communicatively coupled to receive sensor data from the one-dimensional sensor array and send control signals for controlling movement of the motorized motion platform, the computer system being configured to perform operations comprising: 
 (a) controlling the motorized motion platform to move the scanner across a surface of a target object from a starting location to an ending location along a path; 
 (b) acquiring successive sets of sensor data at a known capture rate as the scanner moves along the path during operation (a); 
 (c) converting the successive sets of sensor data to respective scan strips of scan image data; 
 (d) constructing successive scan images from respective sequences of scan strips converted from sensor data acquired as the scanner moves along the path during operation (a); 
 (e) filtering the successive scan images to isolate a feature of a specific type using filter threshold values for depth and intensity which are associated with the feature, wherein the path along which the scanner moves during operation (a) is adjusted based on results of the filtering; 
 (f) finding feature points in respective pairs of successive scan images; 
 (g) determining which feature points found in operation (f) are common feature points in the respective pairs of successive scan images; 
 (h) computing pixel position differences between respective positions of common feature points in the respective pairs of successive scan images; 
 (i) computing respective scanner displacements by multiplying the respective pixel position differences computed in operation (h) by a scaling factor representing a distance traveled by the scanner per scan strip; and 
 (j) computing coordinates of successive positions of points on respective portions of the surface of the target object corresponding to the successive scan images based on the respective scanner displacements. 
 
     
     
       17. The system as recited in  claim 16 , wherein the computer system is further configured to perform operations comprising:
 (k) comparing respective scan images corresponding to the start and ending locations of the scanner; 
 (l) determining a location offset of the ending location from the starting location; 
 (m) computing corrected coordinates of successive positions of points on the respective portions of the surface of the target object corresponding to successive scan images based on the location offset; 
 (n) associating the corrected coordinates with the successive scan images; 
 (o) computing corrected angles of successive orientations of the respective portions of the surface of the target object corresponding to the successive scan images based on the location offset; 
 (p) associating the corrected angles with the successive scan images; and 
 (q) storing the successive scan images and associated corrected coordinates and corrected angles in a non-transitory tangible computer-readable storage medium. 
 
     
     
       18. The system as recited in  claim 16 , wherein the motorized motion platform is configured to enable holonomic motion. 
     
     
       19. The system as recited in  claim 16 , wherein the motorized motion platform comprises a frame and a turret rotatably coupled to the frame, and the scanner is affixed to the turret. 
     
     
       20. A method for tracking a location of a scanner having a one-dimensional sensor array in a frame of reference of a target object, the method comprising:
 (a) moving the scanner across a surface of a target object from a starting location to an ending location along a path; 
 (b) acquiring successive sets of sensor data at a known capture rate as the scanner moves along the path during step (a); 
 (c) converting the successive sets of sensor data to respective scan strips of scan image data; 
 (d) constructing successive scan images from respective sequences of scan strips converted from sensor data acquired as the scanner moves along the path during step (a); 
 (e) finding feature points in respective pairs of successive scan images; 
 (f) determining which feature points found in step (e) are common feature points in the respective pairs of successive scan images; 
 (g) computing pixel position differences between respective positions of common feature points in the respective pairs of successive scan images; 
 (h) computing respective scanner displacements by multiplying the respective pixel position differences computed in step (g) by a scaling factor representing a distance traveled by the scanner per scan strip; 
 (i) computing coordinates of successive positions of points on respective portions of the surface of the target object corresponding to the successive scan images based on the respective scanner displacements; 
 (j) comparing respective scan images corresponding to the start and ending locations of the scanner; 
 (k) determining a location offset of the ending location from the starting location; 
 (l) computing corrected coordinates of successive positions of points on the respective portions of the surface of the target object corresponding to successive scan images based on the location offset; 
 (m) associating the corrected coordinates with the successive scan images; 
 (n) computing corrected angles of successive orientations of the respective portions of the surface of the target object corresponding to the successive scan images based on the location offset; 
 (o) associating the corrected angles with the successive scan images; and 
 (p) storing the successive scan images and associated corrected coordinates and corrected angles in a non-transitory tangible computer-readable storage medium.